Earthquake Resistance of Pipeline With Local Metal Loss Subjected to Cyclic Loading

In this study, nine full-scale experiments were carried out to evaluate earthquake resistance of pipeline with local metal loss subjected to cyclic loading. The test pipes were API 5L X42 with a 762 mm diameter and 12.7 mm wall thickness. Each test pipe had an artificial local metal loss on its outer surface. Each test pipe was machined to have different size of the local metal loss. An internal pressure was hydraulically applied to 2.0 MPa in order to simulate an operating pipeline. A cyclic loading was applied in the axial direction. The strain amplitude of the cyclic loading was 0.5 % because pipelines are designed so that the maximum strain in a straight pipe should be less than 0.5 % during a severe earthquake in Japan. In all the experiments, buckling deformation was observed around the local metal loss after several cycles. The size of the local metal loss influenced the critical number of cycles for buckling. In the author’s previous investigation, the size of the local metal loss affected the peak load strain in pipelines subjected to axial compressive loading. The peak load strain of a pipeline with local metal loss was calculated using an FE analysis. The FE analyses were then conducted under an axial compressive loading using the same test pipe geometry as in the experiments. These experimental and FE analytical results indicated that the size of the local metal loss influenced both the critical number of cycles and the peak load strain. Furthermore, there is a relationship between the peak load strain under an axial compressive loading and the critical number of cycles. Consequently, the earthquake resistance was evaluated for a pipeline with local metal loss subjected to cyclic loading using the peak load strain under an axial compressive loading. Finally, we proposed the allowable size of a local metal loss for a pipeline to have a sufficient earthquake resistance.